We are examining 3 specific hydroxylation reactions that occur in the metabolism of aromatic compounds. These three reactions and the biological system which accomplishes these reactions are: (1) the ortho-hydroxylation of cinnamic acid by chloroplast preparations from M. alba; (2) the p-hydroxylation of cinnamic acid by microsomes from higher plants; (3) the N-hydroxylation of tyrosine, phenylalanine, valine and isoleucine by cyanophoric plants. BIBLIOGRAPHIC REFERENCES: I.J. McFarlane, E.M. Lees and E.E. Conn (1975) The in vitro biosynthesis of dhurrin, the cyanogenic glycoside of Sorghum bicolor. J. Biol. Chem. 250, 4708-4713. M.A. Rosen, K.J.F. Farnden, E.E. Conn and K.R. Hanson (1975) Stereochemical aspects of the biosynthesis of the epimeric cyanogenic glucosides Dhurrin and taxiphyllin. J. Biol. Chem. 250, 8302-8308.